The best way to tell if it's a crack is to climb about 5 meters above it and take a whipper. If it doesnt break, then you'll know it's just a scratch!

Seriously though, if in doubt at all, rather destroy the gear. Take a hacksaw and cut it in half so it cannot be used again. No point in taking chances...and, if you drop any gear and it falls hard onto rocks, do the same.